Most polymer solutions exhibit shear thinning (or pseudo-plastic) behavior while simpler, low molecular weight fluids, such as hydrocarbons and water exhibit Newtonian behavior. It was found that solutions of associating polymers can, on the other hand, exhibit shear thickening (or dilatant) behavior regardless of their molecular weight if they are prepared in given concentration ranges. These concentration ranges can be shifted by adding cosolvents that are capable of changing the associating strength or nature according to a criteria that is disclosed below. By properly choosing the cosolvent and adjusting its concentration, the viscosity range of the fluid, as well as its viscous behavior with time under shear, can be altered.
Polymeric materials are useful as viscosity enhancers when dissolved in the appropriate solvent system. The principle reason for this behavior is due primarily to the large volume which a single macromolecular chain can occupy within the solvent. An increase in the size of the chain produces a concomitant enhancement in the solution viscosity. However, when the polymer chain is placed in a shear field, segmental orientation takes place in direction of the shearing force. The viscosity of the fluid dramatically drops due to this orientation phenomena. This is a typical behavior of most solutions containing dissolved polymeric materials. However, if the polymer molecule has a high molecular weight with a relatively flexible backbone and the solvent viscosity is sufficiently high, different behavior is anticipated.
It has been shown by several groups that, with increasing shear rates, the viscosity should show a decrease, followed by a minimum value and a subsequent mild increase in cases where both solvent viscosity and polymer molecular weight are very high. This latter effect gives rise to a mild dilatant behavior. However, the above-mentioned conditions required for the appearance of shear thickening behavior in these polymeric solution systems are not applicable for many technologically interesting fluids. In most of the common synthetic polymers, it is difficult, from a synthetic viewpoint, to obtain sufficiently high molecular weight and, in addition, most solvents (for example, water) have rather low viscosities.
This invention discloses the novel and unexpected result that solutions of sulfonated polymers, which are soluble in a system of an organic liquid are capable of enhancing the viscosity of these solutions under relatively broad shear conditions. With these unique polymeric materials, dilatant behavior occurs in fluids which are of extreme technological utility. It is further observed that under the identical experimental conditions, the viscosity of the individual copolymer components show the normal shear thinning behavior.
The modification of fluids with polymeric additives is of extreme importance in many technological applications. If such a modification can result in a dilatent behavior, additional advantageous applications can result. For example, substantial shear thickening can be useful in antimisting applications where a stream of the modified fluid should not break into a fine mist, particularly if the stream is produced under a shock situation. Such a shock situation also causes flow with high shear rates which will thicken the fluid and prevent the production of a fine mist. The addition of the polymeric material to the jet aviation fuel improves the antimisting properties of the jet avaiation fuel, such that upon subjecting the jet aviation fuel to a shock situation the jet aviation fuel will gel. Another example is lubrication under high shear rates, where a higher viscosity produced by the high shear rates can help in more effectively separating moving surfaces from coming into contact.